Capacity control for compressors



y 1958 K. M. GERTEIS 2,836,345

CAPACITY CONTROL FOR COMPRESSORS Filed Feb. 26, 1954 3 Sheets-Sheet l INVENTOR. 6%,;

BY m y May 27, 1958 K. M. GERTEIS CAPACITY CONTROL FOR COMPRESSORS 3 Sheets-Sheet 2 Filed Feb. 26, 1954 INVENTOR. K 42 MGMZLQ,

United States Patent 2,336,345 Patented May 27, 1958 CAPACITY CONTROL FOR COMPRESSORS Karl M. Gerteis, Syracuse,

Corporation, Syracuse, N. ware N. Y., assiguor to Carrier Y., a corporation of Dela- This invention relates generally to reciprocating compressors and more particularly to an improved device for automatically controlling the capacity of the compressor in relation to the demand made upon the compressor.

More specifically, the invention relates to an improved capacity control system for use with reciprocating compressors of the type used in refrigeration systems, which control system includes at least one power motivated element capable of unloading a cylinder of a compressor by holding the suction valve of the cylinder temporarily open. The system is generally similar to that disclosed in United States Letters Patent No. 2,626,099, issued January 20, 1953, in the name of Carlyle M. Ashley and includes a control valve for selectively operating the various power elements and a regulating valve, operable in response to a change in load on the compressor, for the control valve.

The chief object of this invention is the provision of a capacity control system of the type described which includes means for operating the system dependent upon a predetermined condition existing within the compressor. The capacity control system is preferably actuated by oil pressure in the lubrication system of the compressor and the means mentioned above includes an arrangement which prevents the system from operating unless the oil pressure in the lubrication system has reached a predetermined amount. This particular feature also becomes important during the time in which the compressor is started, and also in the event the lubrication system fails to produce pressure of a predetermined value. The arrangement forming a feature of this invention prevents the capacity control system from further operation by causing the cylinders equipped with unloaders to become unloaded thereby reducing the load on the machine.

Another object of the invention is the provision of an improved control valve for use in the system which includes an unique construction preventing rapid cycling of the cylinders in response to load variations. This condition occurs when, for example, the reduction in load is sufficient to cause a cylinder to unload but the reduced output of the compressor is insufficient to meet the reduced load requirement.

One instance where a compressor capacity control systern having a time delay feature, of the type to be described, is particularly useful, occurs when the compressor motor must be started by applying the current thereto in step or stage fashion. Under these circumstances the current used to start the motor is delivered to the motor in successive increments to certain windings. To prevent the motor from stalling under a load supplied by the fully loaded cylinders, the unloader elements are temporarily isolated from the lubrication system by the action of a time delay feature, to be described. Therefore it will be appreciated that the motor will not be subject to the loading due to the action of the loaded cylinders until the starting operation has reached a stage capable of operating under such a load.

Other objects and features of this invention will be apparent upon a consideration of the ensuing specification and drawings wherein Figure l is a diagrammatic view illustrating a compressor including the capacity control system of the present invention;

Figure 2 is a view partly in elevation and partly in section illustrating means for disposing the suction valve of a cylinder in an inoperative position;

Figure 3 is a sectional view of the control valve;

Figure 4 is a sectional view of the regulating valve, showing the improved safety feature forming the invention;

Figure 5 is a view similar to Figure 4 showing the operating parts of the regulating valve in a different position; and

Figure 6 is a diagrammatic view illustrating the manner in which the individual elements of the improved capacity control system are related.

Briefly, the capacity control system includes one or more cylinder unloading elements, depending on the number of cylinders present, in communication with a common control valve having a spring urged piston movable in a passage in such manner as to permit the application of oil pressure to certain of the unloader elements. Movement of the piston in the passage is dependent upon an unbalanced force between the spring and a source of oil, the pressure of which is under the influence of a regulating valve, which in turn is subject to the load on the compressor as evidenced by the suction pressure to which the compressor is subjected. The oil under the influence of the regulating valve is a part of the lubrication system of the compressor and one feature of the invention involves preventing the passage of this oil to the control valve until the pressure in the lubrication system reaches a predetermined minimum value, and also preventing any attempt to unload when the oil pressure to the unloader is insufficient to positively eflect operation of the unloader. This permits a more efllcient operation of the valve for the reason that the oil, once it enters the control valve, to act in opposition to the spring, is not subject to variations due to inadequate pressure in the lubrication system.

As pointed out above, the operation of the control valve is dependent in part upon the demand upon the compressor and causes the individual cylinders to load or unload in accordance therewith. Changes in the load upon the refrigeration system as reflected by the pressure in the suction line, however, tend to be small in comparison with the change in capacity of the compressor when, for illustration, one of two operating cylinders is unloaded. it will be appreciated that the capacity of the compressor may be reduced by 56% at this point. The compressor tends to balance against the load so that the unloaded cylinder is rapidly loaded again, resulting in an action known as cycling. Rapid cycling often causes undue wear on the parts involved and should be avoided or at least minimized. To accomplish the elimination of rapid cycling, this invention includes an improved control valve, incorporating a lost motion feature which necessitates a relatively large suction pressure change before the capacity control system changes from unloading to loading or vice versa after operating through a pattern that includes either successively loading or unloading, while permitting a relatively small differential to occur for the purpose of functioning in the latter manner. in other words, when the capacity control system operates L0 chang from loading to unloading or vice versa, a relatively large difierential in suction pressure is necessary before the change occurs. 7

Referring to the attached drawings, there is illustrated in Figure 1 a compressor 2 having a plurality of cylinders 'pressor'usedftcr illustration in a i which forms no essential part of the tion and includes a lifter sleeve 10 surrounding .lower portions of the pins 13 r V thersleeve 19.

i therewith, and a bottom plate communicating with line 21.

7 may seep between the 7 spring 25 in the casing.

' impoSedupon the compressor.

prises a casing 37, consn'tuting a is oil sump 5 for'the operating mechanism'of the com- 7 pressor including crankshaft 6, piston 7, and connecting rod 8 all of which are elements of a conventional comrefrigeration system 7 invention but which, it will be understood, are presentto form an operable compressor.

' It will be appreciated that eflicient operation of the compressor necessitates varying the output of the com pressor in accordance with the demand made thereon. One convenient method of varying the output of the compressor involves equipping certain of the cylinders with an unloader element as of the type illustrated in Figure 2. .Theunloader mechanism disclosed is utilized to place the'suction valve 14 of the cylinder7 in inoperative posithe cylinder and being provided with an outwardly extending fiang'e 11. The sleeve is adapted to move in a reciprocatory manner about the outer surface of the element from a'lower limit as indicated by band 12 embracing the cylinder. V

. Disposed radially about the flange 11 and in engagement with the upper surface thereof are a plurality of litter pins13 which operate to lift suction valve 14 from its seat in valve plate 15 in'response to the upward movement of'the sleeve 10. Loading springs 16 surround the bottoms of the pins in engagement with the flange 11 on 'Movement of the sleeve 10 is provided by a power element comprising a forked lever 17 having'the end portionsinfengagernent with the underside of flange 11 and which is pivoted at its. other end to a vertical rod member 18; .The latter member is secured at its other end to piston 19 which moves within casing 29 in response to oil'pressure introduced therein through line 21 in and serve to maintain the to the regulating valve in a manner to be morecom- I the manner to be laterdescribed. Casing is provid ed' lever support 22". integral 23, having an opening 24. A spring member 25 'encircles the vertical rod 18 and bears against the top memher 22 of the casing and the piston '1) as shown in Figure 2so as to normally urge the piston to its lowermost position within the casing. Opening 26 is provided in casingZt) and is designed to accommodate oil which piston and the wall of the'casing. Thus, it may be seen that the power unloading element is so constructed and arranged as to cause the lifting pins 13 to move the suction valve 14 from its seat when there is inadequate oil pressure'to overcome the action of the. When adequateoil pressure is' 19 istorced upwith a top plate 22, having supplied to the power element, piston 'wardly against the action oi the spring 25 pivoting lever 29 having afirst end'member 30 and a wardly and allowing springs 16 to move lifting pins 13.

downward so that valves.

Control valve 28 com secondend member 31. 'The casing 29 is provided with a cylindrical bore 32 extending therethrough which accommodates a movable piston 33fhaving a head 34 and a hollow elongated shank 35, having its unattached end open, dependingtherefrorn. Bore 32 is in communication with a socket 36'positioned within end member 30 and which is provided with a porton of reduced diameter spring "seat; One .end of a spring port168'then the .full'pressure in the lubrication system is p exerted ,by spring in efiect forms a radial projection about the shank. Mounted within'the bore 32 so as to surround'the shank 35 of piston 33 is a bobbin 40, having a'first enlarged end portion 41 providing a sealing engagement withthe sides of the casing which define bore3'2, an intermediate portion 42 of reduced diameter end, an end portion 43,

including a sealing surface 45, the exterior surfaceofwhich is formed bya series of alternately spaced grooves and ridges or lands 44 and 45.

Casing 29 has further provided therein radial'bores 46 extending from bore32 through the side or the casing and through a boss 47 located on the external surface of the casing. A pin 48 projects through aligned openings 49 providedin the boss 47. Seated against pin ,48 -is a spring member 49" having the outer end thereof 'in'en gagementfwith aspherical ball 51, the parts being so de signed and constructed that the balls 51 i urged inwardly of the casing into engagement withthe grooves is 'a radial opening is further provided'with a seires of radial openings 52 through which oil from the lubrication system of the compressor-passes en route to the individual unloading elements mentioned. above in an opening 54 for the reception of line 55 connected pletely described. 1

a Figure '4 illustrat valve includes a first casing member 56' which includes a system of passageways which direct and guide oil froni 7 through the regulating valve and.

the lubrication system to 'thecontrol. valve insuch a manner as to move piston may be endiof which contains an internally threaded 'socket which is adapted extension. 58 oi chamber 59. [Disposed within chamber 59 is a bellows '60 subjected on one side to' suction pressure through inlet, '61. The opposite side of bellows '64) is subjected to a predetermined force exerted by spring 62. The force 62 may be adjusted by means of stem 63 'mounted within a threaded 'block 64 which is equipped with a cap 65. Inaddition, such side of the bellows is subject to atmo'spheric'pressure. Mounted within socket 66 of casing 56 is a needle valve 67 which a is normally urged to the left of the valve as viewed in Figure '4soas to close port 68 serving as one extremity of a passageway 69. .The needle is urgedto this position by action of spring 70. *Acting in opposition to the spring 70, through push rods 71,

constructed-and;designed that the addition to or subdenced by the suction pressure on the bellows member 60,- are such that the needle valve completely. closes the V employed'to force oilthrough line 55 against head 340i member 38'. is positioned against seat 37 andthe other end of the 'spring38 is in engagement with the'under slde of the head 34 so as to normally urge piston 33 to the leftof the control valve as viewed in Figure 3. Open piston-member33, forcing the latter element against the action "of spring 38 to the right as viewed in Figure 3 in a manner to be later described. Under these circumw stances, the parts are so designed and constructedthat oil j 7 pressure from the lubrication system entering the casing i 29 through line 53 passes through the various ports and passageways 52 to the unloader elements. However, one feature of my'invention involves obstructing the passage serves to vent oil to the crankcase when the piston V are normally 44 on bobbin 40. Also positioned in casing 29' V 53 in'communication with the main supply line of the lubrication system. The'casing' 29 Cover 31 has provided there- H s a' preferred form of a regulating valve56 -to be used in the capacity control system. .The I to cooperate with an externally threaded V the casing56' so as to form therewith is the bellows 60, under the influence of spring 62. The individual parts are so.

of oil pressure to the control valve until the pressure in the lubrication system reaches a predetermined figure. To accomplish this, one preferable form of construction includes, in the casing 56' ofrthe regulating valve, a cylindrical bore 72 having an opening which is closed by plug 73, and which has assembled for movement therein a piston 74, adapted to be urged toward plug 73 under the influence of a spring 75. The spring has one end abutting against the piston and the other end seated against the end of bore 72. The piston 74 is provided With a diametral bore 76, in which is positioned a coil spring 77 tending to force two ball bearings 78 into annular grooves 79 formed on the wall of the bore 72. The piston has the external surface thereof provided with a series of spaced grooves 80 and lands 81 as Well as an axial projection 81' and is so constructed that under the influence of the spring 75 the piston is projected across an opening 82 which is in communication with line 55.

The position of the piston 74, in the absence of oil pressure, in the lubrication system of a magnitude sufficient to overcome the action of the spring, is shown in Figure 5 wherein the axial projection is in engagement with the inner surface of plug 73, so as to form a chamber 73.

When the oil pressure in the lubrication system reaches a predetermined value, the action of the spring 75 is overcome and the piston is moved to the retracted position within bore 72 as shown in Figure 4. The bore 72 is in normal communication with the lubrication system of the compressor through line 83 which is connected to the main lubrication line 85.

After the oil pressure in the lubrication system reaches a value suificient to overcome the action of spring 75 so as to force piston 74 to the left of the bore as viewed in Figure 4, opening 82 is placed in communication with bore 72 and the opening 88, the function of which will be explained later, is blocked. The opening 32 permits oil to flow through passageway 69 to the port 68 and also into the chamber 87 which is in communication with line 55. The oil then flows through line 55 to the control valve where its action is as described above. When the piston 74 is in extended position (see Figure 5) opening 88 connects bore 72, with chamber 87 permitting line 89 to vent oil to the crankcase. Thus the opening 88 serves as an escape outlet for oil which may be trapped in the circuit between the control valve and the regulating valve. For illustration, assume that the oil pressure in the lubrication system has dropped to the extent that spring 75 forces piston 74 to its extended position, blocking opening 82. Under these circumstances, the piston 33 in control valve 29, under the influence of the spring 38, is forced to the left as shown in Figure 3, so that oil in chamber 32 is forced through line 55, chamber 87, passageway 88, and through line 89 to the crankcase.

In order to delay the operation of the needle valve 67 in the regulating valve, it may be desirable to include in the construction, a surge chamber of the type disclosed in co-pending application Serial No. 308,254 filed September 6, 1952 in the names of Lars Hanson et al. As shown in Figure 6 the chamber 90 is formed in the end cover of the compressor and is provided with a cover 92 in the manner shown. A firstopening 94 in the cover permits oil at crankcase pressure to be introduced into the charnher and a second opening 96 communicates with a line connecting the chamber and the regulating valve. Under this arrangement changes in the suction pressure in the compressor will be transmitted to the regulating valve, through the chamber which acts in the manner of a daunpening agent, thereby delaying the transmittal.

In order to more adequately describe my invention, the operation thereof will be explained. When the compressor is started, the power unloader elements, because of a lack of oil pressure, are arranged with the sleeve in its uppermost position and pins 13 holding suction valves 14 in inoperative position so that the output of the rection is prevented by piston 74. Oil is also delivered from the main line 1 through line 53 to the control valve 28.. Due to the absence of oil in line 55, the piston 33 together with bobbin 40 are positioned within the control valve in such a manner as to prevent passage of the oil from line 53 through any of the openings 52. The action of spring 38 moves the piston 33 to'the left of the valve as shown in Figure 3 and the annular ring 39 engages flange 41 of the bobbin, so that the flange 41 is positioned within the opening 32 between opening formed by the line 53 and the closest opening 52.

After the oil pressure in the lubrication system has been built up to a pressure suflicient to overcome the action of spring 75, the piston 74 is moved to its retracted position, in the manner shown in Figure 4. This is accomplished by the oil in line 83 entering bore 72 through grooves 80, seeping past the lands 81 into chamber 73' where the pressure gradually builds up to a value suflicient to overcome the force of the spring 75. Oil is also free to seep to the left of the opening 83 in bore 72; however, it is vented to the crankcase through opening 88 and line 89. Because of the presence of the spring actuated ball bearings 78 and the grooves 79, the.

force necessary to project or retract the piston 74 over outlet 88 is abrupt and may be considered as snap-acting. This arrangement prevents any amount of oil other than that under pressure suflicient to properly actuate the control valve 28 from entering line 55. Oil is now free to flow through opening 82, to the control valve 28, via line 55. It is also free to flow to the port 68. The needle valve, at start-up, practically closes the port because of a high suction pressure condition prevailing so that the full pressure of the lubrication system will be exerted against the head 34 of piston 33, in opposition to the action of spring 33. The needle 67 is moved out of engagement with the port 68 in response to a reduction of the suction pressure within the suction manifold of the compressor and will move back to close the port 68 with a rise in suction pressure. The suction pressure is indicative of the load being placed upon the refrigeration system so that the pressure exerted against the head 34 of piston 33 in control valve 82 is varied in response to the amount to which needle 67 restricts port 68. Thus it may be seen that the pressure of the oil in engagement with head 34 is subject to the action of the regulating valve. The strength of spring 38 may be varied in accordance with the pressure within the lubrication system so that the various ports of opening 52 are opened and closed in accordance with the pressure varying in line 55.

Assuming, during operation, the lubrication pressure drops below a minimum value, the piston74 is immediately moved under the action of spring 75 to its extended position so as to block passageway 82 thereby causing a substantial reduction in oil pressure in the line so that piston 33 moves rapidly under the influence of spring 38 to close 01f the passageways 52 leading to the unloader elements. Thus, it maybe appreciated that chattering of the suction valves in the individual cylinders due to inadequate oil pressure being maintained in the unloader cylinders is obviated.

Another very important feature of the invention resides in the particular piston construction shown in Figures 4 and 5. The alternate grooves'and lands on piston 74 prevent the piston from being forced upward against the bore by permitting oil to flow around the piston so that any tendency for the piston to become lodged in the cylinder is obviated.

Summarizing, it will be obvious that, by virtue of the construction disclosed herein, the successive loading of closed serves merely as an illustration; of

' her and the regulating means.

7 thetcylinders will take place as theindividual openings'52 of controlvalve 28 are placed in communication with opening 53 through the movement of the bobbin fl'and the pistonr33. If, however, the load on the compressor isldiminish'ed, the pressure against piston 33 will likewise diminish due to the variation in suction pressure causing needle 67-to move away from port 68,f thereby reducing the head under which the oil, in pressure contact with piston 33, is subjected. -The'action of spring 38 forces the piston 33 to the left of the-control valve as received intFigure 3, however, bobbin 40 does not move 1' to the left until the radial projection 39 engages it. I Thus it will' be noted that a pressure change of a magnitude suificient-to move the;piston:an amount equivalent to theedistance from, the right end of the bobbin to'the radialprojection 38 is necessarybefore any of the openings 52 are to he afiectedwhile on 'the other 'hand the pressure change against piston 34 necessary tomove the piston in the direction currently moving is relatively slight.

The particular lost motion type of connection between the bobbinp40 -and piston 33 permits the attainment of this feature; H; 7.1 t m It will be apparent that my invention may be incorporated;in other construction without departing from the spirit andscope thereof. .For illustration a separate valve for performing the functionof the piston 74'may be in corporated in the capacity control circuit. It will therefore be appreciated that the construction, herein disthe invention and not a limitation thereof. t t a I claim: a i a i 1. In a system of capacity control fora reciprocating compressor having a lubrication system, the combination of means adapted to hold compressor valves in inoperative position, means for actuating thefirst means to hold the compressor valves in inoperative position, a control member for. governing operation of the second means,

means for regulating the control member in response to conditions of load imposed upon the compressor, and means including a line in communication with the lubrication system controlling the operationof the control mem- 72. The system descnbed in claim wherein the controlling means is responsive tooil pressure in the lubrication system of the compressor.

' 3. In a, system of capacity control compressor having a lubrication system, the combination of an oil pressure actuated element for holding a cornpressor valvein inoperative position, oil pressure actuated means for permitting or discontinuing the passage of oil to'said element, means responsive to load conditions for varying the oil pressure'imposed on the pressure actuated means topermit or'to discontinue the'passage of oil to said element in accordance with load conditions and meansincluding a line in communication with the lubricationtsy'stem a cylinder and a piston movably mounted ficient to'elfect positive operation of said oil pressure actuated element, for obstructing the passage of oil to said oil pressure actuated means andsaid load condition responsive means. I f

4. A:capacity control system as set forth 'in claim 3 7' wherein said last mentioned means is vresponsive to the oil pressure in the lubrication system of the compressor. 55A capacity controlsystem as set forth in .claim 4 wherein said last mentioned means deactivates the oil pressure actuated means when the pressure in the oil lubrication-system of thecompressor is reduced below a predetermined value,

In a system of capacity controlpfor a reciprocating U compressor having a lubrication system,v the combination of' an' oil pressure actuated element for holding a com-. "pressor valve in inoperative position, oil pressure actuated l means; for permitting or discontinuing'the passage of oil tolsaid elemen'umeans responsive to load conditions'for varying the oil pressure imposed on the pressure actuated for a reciprocating means to permit or to discontinue the passage of oil to said element in accordance with load chnditiongand means including a line in'communication with the lub'ricationsystemafcylinder and a piston movahly mounted therein'for obstructing the; flow of oil to said, oil pressure actuated means in response 'to oil pressure in thelubri cation system insuflicient to effect positive; operation .lof

' the oil actuatedelement.

compressors, a combination of'oil pressure actuated ere:

ments for holding compressor valves ininoperative 'position, an oil pressure actuated valve permitting or ,discontinuing the passage of oil to said elements, and 'a second valvefor varying the oil pressure imposed on t a the first valve, said first valve including a chamber having a series of outlets connected to said elements, said chamber being tprovided with an opening in one end permite I ting passage or oil from the lubrication system 'of' the compressor thereto, a pi'ston' movable in said chamber,

said piston being provided with a head portion-adapted to fsnugly fit the sides of said chamber, and 'a socketed shank portion dependingitherefro m,yieldable means, exl tending within said socket having one end bearing against said piston head and the other end seated atthe end of said chamber, said'yieldable means adapted to force said piston toward one end of said chamber in'o ppo sition to the pressure of the oil in the'lubrication'system, and annular ring embracing 'said shank portionof saidpiston adjacenttone end thereof so :as to provide a'radial'projection, a circular sleeve, surrounding said piston shanlr between said 'head portion and said ring, having enlarged end portions adapted to engage the side of said chamber, said sleeve being of shorter length; than the distance on said piston shank between the head andjring,

andmovable within said chamber in response to move-' ment of the piston thereim'said sleeve movement being delayed when a change in the direction of movementof said piston occurs. t l l l t 11. In a system of capacity control for reciprocating compressors, a combination of oil pressure actuated ele-l ments for holding compressor valves'ininoperative posi tion, an 'oil pressure actuated valve adapted to permit the passage of oil to said elements insequence, said oil pressure actuated valve including, a casing having a series of radial passages therein, said passages being in cornmunt ication with a piston accommodating chamber,. a piston mounted within said chamber, and a sleeve surrounding said piston adapted to permit communication between" certain passages in response to movement of said piston. .f 12. In a system of capacity control for reciprocating compressors, a combination'of oil pressure actuated ele-* ments for holding compressor valves in inoperative position,'an oil pressure actuated valve adapted to permit the passage of oil to said elements in sequence, said oil pressure actuated valve includinga casing having a*passageway therethrough, a first opening inoneside of said casing permitting fluid under pressure to enter said casing,

a plurality of ports positioned'inthe'side lof said'casing; 'an inlet in one end of said casing permitting oil under pressure, dependent upon theload on thecompres'sbr, to, l enter said passageway; and means includinga piston posi- 'tioned within said passageway so as to permitcomniunication ofsaid oil passage in sa i'd casing with said radial 1 ports in'accordance with the position of said piston within asset forth in claim-'8 said passageway, the force required to change the direction of movement of said piston being greater than the force necessary to move said piston in one direction.

13. In a system of capacity control for reciprocating compressors, a combination of oil pressure actuated elements for holding compressor valves in inoperative posi tion, oil pressure actuated means for permitting or discontinuing the passage of oil to said element, means responsive to load conditions for varying the oil pressure imposed on the pressure actuated means to permit or to discontinue the passage of oil to said element in accordance with load conditions, said oil pressure actuated means including a chamber having a plurality of outlets connected with said elements, a piston movable in said chamber, means for imposing a predetermined pressure on said piston to move the piston longitudinally in one direction in said chamber, and means surrounding said piston, adapted to isolate certain outlets in response to movement of the piston Within said chamber.

14. In a system of capacity control of the type referred to in claim 13, wherein said last mentioned means forms a lost motion connection with said piston, so that a delay in the operation of said means in response to movement of the piston occurs.

15. In a system of capacity control for reciprocating compressors the combination of means adapted to hold compressor valves in inoperative position; means for actuating the first means to hold the compressor valves in inoperative position; a control member for governing operation of the second means; and means connected to the lubrication system of the compressor for reguiating the control member in response to conditions of load imposed upon the compressor, said last mentioned means preventing operation or" said control ember when the pressure of the lubrication system of the compressor is insufficient to cause positive operation of the compressor valve holding means.

References fired in the tile of this patent UNITED STATES PATENTS 1,354,580 Schumacher Oct. 5, 1920 2,011,333 Clifton "Aug. 13, 1935 2,305,519 Dunmire Dec 15, 1942 2,615,671 Landon Oct. 28, 1952 2,638,265 Newton May 12, 1953 2,673,025 Labus et al Mar. 23, 1954 FOREIGN PATENTS 634,803 Great Britain Mar. 29, 1950 UNITED STATES PATENT @TTTQE CERTIFICATE 9F "GORBECTIQN Patent No 2, 836,345 May 271 1958' Karl M, Ger'teis It is herebjr certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 70, for por'tom' read portion e; column 7, line 56, for "a cylinder and a piston movably mounted" read ea operable in response to oil pressure insuf= Signed sealed this llt-lz day of November 1958,

' (SEAL) Attest:

KARL 222mm ROBERT C. WATSON Attesting Ofi'iccr Qommissioner of Patents 

